Casting Materials FAQ
The alginate mold is the "negative" of your object. The idea is to pour some type of casting material into the mold to create a "positive" sculpture of your object. We get all kinds of questions about this. Here are some answers:
What casting materials can I use?
Acceptable casting materials are:
- Plaster of Paris (really too soft for most applications)
- LiquiStone (really perfect for most applications- but hard and stiff)
- Other Gypsum Cements (Hydrocal, Hydrostone- anything over about 6,000 psi strength)
- Forton FG (This fortified gypsum product can be "filled" with various metal powders)
- Silicone (expensive and you MUST use the "platinum catalyzed" silicone or it takes too long to set)
- Urethane (must use very quick setting urethane)
- Wax (works fine- but be careful- its hot and stays that way for a while)
Casting materials with which alginate has problems:
- Acrylic resins (the water in the mold tends to cloud the surface)
- Tin-catalyzed silicone (takes way too long to set up- mold distorts)
- Metals (poured metals boil out the water and destroy the mold quickly)
- Any casting material that would be adversely affected by a moist mold)
We encourage you to experiment and let us know if you find something new. We'd love to share it with the world.
Why should I use LiquiStone?
1) Its easy to mix
Add the powder to the water slowly while mixing with a whisk or stick. It is easy to adjust the viscosity with a little extra water or a little extra powder.
2) Its easy to work with
When mixed thin- it pours easily. Pouring slowly minimizes air bubble entrapment. Great for hand castings.
When mixed more thickly- it can be built up on surfaces that are not horizontal. Great for torso and face casting
3) It sets fairly quickly
LiquiStone will give you about 13-15 minutes of working time and it will achieve 90% of its final strength within 1 hour. Most castings can be unmolded in one hour. This can be accelerated to as little as 30 minutes by using a plaster slurry as your "mix water".
4) It sets quite hard and durable
LiquiStone sets to between 7,500 and 8,000 psi strength- which is 10 times as hard as Plaster of Paris. You will not be able to scratch LiquiStone sculpture with your fingernail. These sculptures can last for generations.
5) The bright white color is great for painting
Paints and finishes that are slightly transparent can be very beautiful. The light goes through the finish, bounces off the white surface and returns through the finish.
How much LiquiStone Do I Need?
Here are some guidelines for portioning LiquiStone for your particular project.
Remember, it is always better to have just a little bit "too much" LiquiStone then "not quite enough".
|Baby Hand||0.5 lb|
|Child Hand (3 yrs)||0.75 lb|
|Child Hand (8 yrs)||1.0 lb|
|One Adult Hand||2.0 lb|
|Two Adult Hands||3.5 lb|
|Two Adults/Two Children||6.0 lb|
|Adult Foot (each)||4.0 lb|
|Half Torso||4-6 lb|
|Full Torso||8-10 lb|
LiquiStone Water/Powder Ratios
A good general rule of thumb is to use 2.3 times as much LiquiStone as water- measured by volume. That means that for every 2.3 scoops of LiquiStone you're going to add 1 scoop of water.
The "scoop" you use can be any measuring device you want. NOTE: An 8 fl.oz. cup of LiquiStone weighs about 250 grams, about 8.8 ounces or about 0.55 pounds.
The Slightly More Precise Answer
As always, there are tweaks you can use for different types of projects to make this better.
There are two different types of molds: Bucket Molds and Layup Molds.
- A bucket mold is like a hand casting where there is a hole to fill with casting material. For bucket molds, we like to have a thinner LiquiStone mix so it flows better into the mold. For a bucket mold use just 2.2 times as much LiquiStone as water.
- A layup mold is like a face casting where the mold is like a bowl. These we like to have a thicker mix so it will stick to the sides of the "bowl" so the edges don't get too thin. For a layup mold use 2.4 times as much LiquiStone as water.
The REALLY Precise Answer
|ounces (weight)||fluid ounces|
|ounces (weight)||fluid ounces|
|1 cup||8 fl.oz.|
|1 pint||16 fl.oz.|
|1 quart||32 fl.oz.|
|1 gal.||128 fl.oz.|
LiquiStone Mixing Techniques
LiquiStone is very easy to mix. There are a variety of techniques that can be used.
Add the half the powder to the water and stir until wetted, then slowly add more stone- stirring the whole time. If you think your final mix is too thin or too thick you have plenty of time to adjust with more powder or more water. Remember, a little water goes a long way.
Up to about 8 ounces you can easily mix LiquiStone with a spatula like our Plastic Spatula.
Up to about 3 pounds of LiquiStone can be mixed with a sturdy kitchen whisk.
Over 2 pounds, it is often easier to mix with a Power Mixer on an electric drill. NOTE: Always make sure the drill is running in reverse (anti-clockwise) to ensure the minimum of air bubbles in your mix.
When mixing LiquiStone for very large projects, work quickly so you can pour a fresh batch of LiquiStone on top of the last batch before the previous batch has hardened.
What Is the Working Time and Demold Time of Liquistone?
Typically LiquiStone has about a 12-15 minute working time before it gets too thick to move around. This can be extended by using very cold water or accelerated by using warm water
Typically LiquiStone has set firmly enough to for the casting to be removed from the alginate in one hour. Under no circumstances should a LiquiStone casting be left sitting in the alginate mold for more than about 5 hours. This can actually degrade the surface of the LiquiStone or begin to cause mold to form.
Accelerating the whole thing
If you think you will be in a rush to get the casting out of the mold use the following steps.
- Measure out your water 1 hour ahead of time
- Throw a handful of LiquiStone into the water and stir it up.
- When it is time to mix the LiquiStone for your pour, use this thin stone/water mix.
The small amount of LiquiStone in the water will form crystals which will act as nucleating sites that will kick the main batch of LiquiStone to set much faster. Be careful because you will have less working time too.
How to Fix LiquiStone Castings
So there's something wrong with your LiquiStone casting? There are several types of problems and lots of ways to fix them.
The types of problems can be boiled down to these:
- "Outey" Bubbles
- Missing fingers
- Broken fingers
- Broken fingernails
- Flattened fingertips
- Rough surface on casting
These are bubbles IN the surface of the casting. These were caused by bubbles in the LiquiStone mix coming to the surface. Usually these are small and easy to fix.
- Mix a very small amount of LiquiStone.
- Thoroughly wet the area where the fix is to be made.
- Put some LiquiStone mix into the hole.
- Wipe it with your fingertip lightly until it is smoothly fixed.
- It might take a little sandpaper to smooth off once it has set.
Usually these are small.
- Sometimes just rubbing your hand across them causes them to roll off.
- Sometimes they can be "popped" off with gentle steady pressure from a knife.
- If they are large you will have to carve them off with a knife. This is where some of the tools in Accu-Cast's LifeCasting ToolKit come in handy.
We go over this very carefully in the literature about hand casting and in the hand casting DVD. The problem is that the fingers in question were bent more than 90° and the fingertips weren't touching anything else when in the molding bucket full of alginate. It is often easier to redo the casting, but if you can't here are some tricks.
- If you can find the part of the original alginate mold where those fingers were it is sometimes possible to carefully pour those fingers separately. They can then be attached to the sculpture using more LiquiStone (since it sticks to itself.
- Other times the defect is very small and in an inconspicuous place. A small amount of LiquiStone can be built up where that fingertip was and carved back to the shape of the fingertip after it sets. This takes some sculptural skills but it is often unnoticeable by anyone but yourself.
Broken fingers are a result of applying too much pressure to them during the unmolding process. This is VERY easy to do with baby and child hand casts. It is also easy to do if you try to rush the demolding of the casting and peel off the alginate before the stone has gotten hard enough.
Broken fingers can be reattached using LiquiStone as the glue.
- Wet both mating surfaces well.
- Mix up a very small amount of LiquiStone.
- Put a little on the broken area and reposition the broken finger.
- It will need to be kept in place while the fix is setting. Often it is possible to prop up the casting in such a way that the finger in question is pointing straight up. It will hold itself in place if you do this.
- Clean off any extra LiquiStone from the joint once it is completely set- about 2 hours.
To avoid broken fingernails it is always advisable to put some clay up under the nails before doing the hand casting. Sculpt the clay so it the nail is about 3x as thick as normal. Sculpt the clay so the nail comes to a proper point at the tip.
LiquiStone is just not strong enough for very thin cross sections like normal fingernails. You can take a nail file and file down the broken nails on the casting or redo it if the nails are really important to the model.
Flattened fingertips are ALWAYS cause by rushing the hand removal from the alginate mold. It is imperative that the suction be released from all fingers before pulling the hand out. There is no way to beat atmospheric pressure and if you struggle to get the hand out the fingertips in the mold will flatten as the hand is pulled out. They are often rough and distorted in other ways when this happens.
Solution? Probably best to redo the mold. If the effect is very small it might be possible to resculpt those fingers by adding LiquiStone as described above in Broken Fingers.
Rough Surface on Casting
A rough surface on the casting can be caused by several things.
- Insufficient mixing of the alginate or LiquiStone.
- Removing the hand from the alginate mold before it is completely set.
- Waiting too long before pouring the LiquiStone into the mold.
Most of the time, this is confined to a small area. Careful use of sandpaper can often solve this issue. If the roughness is extreme or large scale, it is best to redo the mold. Try to determine the cause and do a better job the second time.
How to Paint LiquiStone Castings
So you want to add a "finish" to your LiquiStone Casting. Here's what we've found works best.
IMPORTANT NOTE: Do not apply a finish to a LiquiStone cast until it has dried for several days. In humid climates this process might take a week or more.
You can literally use any kind of paint on LiquiStone. It is the perfect surface to paint.
Spraypaint can be beautiful. Use them in combination to give great effects.
- Antique Gold
- Antique Bronze
- Gloss Black
- Matte Black
We use a Lazy Susan type turn table and spin the casting as we spray it lightly. Its always best to spray in very thin coats. Build up the paint slowly to avoid filling in the fine detail that you captured in your mold like fingerprints.
Also be careful because things that are closer to the spray nozzle (like fingertips) will receive MUCH more paint than things further away.
Also be careful with gold and white spray paints. They have lots and lots of pigment in them and they will fill in detail areas much more quickly than other paints. Go slowly with lots of thin coats.
Experiment with using things like shoe polish, various waxes, oils, tea, coffee, oil and/or water color paint for some seriously interesting effects.